Electrical apparatus



Feb. 1927.

8 v. BUSH ELECTRICAL APPARATUS Filed April '7, 1922 40 skille Patented 111%.' 8.. 1927. l i

"".fJiJNpAlTED ifsrATEs VANNEVAB BUSH, F BEDFORD, MASSACHUSETTS, ASSIGOB, BY HlSNl-ABSIGN- MENTS,

SETTS, A. CQRPQBATION-OF MASSACHUSETTS.`

nLnc'rnIcAL APPARATUS.'

agpueatioa mea Appu- 7; 19225 serial No. 550,519.,l l

'The present invention relates-to electrical apparatus and more particularly to apparatus of the type disclosed in the copending a plication of Bush, Serial No. 510,916,

I filed ctober 27 1921, and Smith, Serial No,

526,095, filed December 31, 1921.,

These applications relate to electrical .ap-

.paratus having cooperating electrodes immersed -in a gas and 'so designed and v-lo- 1l cated with res'ect to :one another that the conductivity o the gas lled space separat-l -in the electrodes may be controlled.

l he Object of the present invention is to improve the construction and operatlon of this type ofapparatus andA to this end one feature of the. invention contemplates the 'provision of closely7 spaced carbon electrodes .immersed vin ay gas, one of the' electrodes. having an opening communicatingwith a hollow lspacebehind the surface of sufficient size to Ypermit formation. of av space charge. A further feature 'of the invention 'contemplates the provision of a hollow carbon electrode provided with an oxide coating il 'upon its active surface to decrease the voltf age drop between the electrodes and increase the ca acity of the tube embodymg these electro es. f f In a simple form of the invention an ox- 80 ide of calcium, barium, strontium, .or mixtures of these oxides, is applied to the surface of the electrode with rosin and the coatl ed electrode is then heated sufficiently to bind the mixture of oxide and rosin thereon.

Still further features of the invention consist in certain novel features of construction,

combinations and arrangements of parts hereinafter described end claimed, the adof which will be obvious to those in the art from the following descri tion.

e accompanyingl ldrawing illustrates a section in elevation of a tube embodying the features of the present invention. v

Fig. 1 is a vertical sectional view of the discharge device.

Fig. 2 is a top vanta planview of the cathode,

@and

Fig. 3 is a cross section'al view through the 5 stem.

The illustrated embodiment of the invention shown in the drawing comprises a hermetically sealed receptacle 10 filled with helium or other suitable gas and having cooperating -electrbdes indicated enerally at 12 and 14:I immersed therein. T e electrode 12 comprises a carbonfdisk -16 having an. openm 18 formed centrally therein surrounde .by a tubular neck 20. The lopening 18 communicates with'a chamber orspace enclosedvby a carbon cup 22 which engages with the surface of thedisk 16-,as indicated,

T0 RAYTHEON MANUFACTURING COMPANY, Oil?4 CAMBRIDGE, MASSAUHU- I and forms Ain combination with the disk a i hollow. electrode with an opening extend-I ingy into the-interior. The carbon disk 16 ing shoulders-'26 formed thereon," theA supports being .connected with rods .which extend upwardly beyond the cup 22 and are -connected above'the cup by wire or. similar material to hold the .cup and disk in asis positioned bya series of supports 24- havf sembled relation, as clearly shown. in the trodes may be conveniently connected to the l -tubein the samemannenas disclosed inthe 'application to Smith, Serial No. 526,095,

hereinbefore, referred to.

Such a tube willconduct current freely4 when the hollow electrodel is negative and will insulate against such conduction when the opposite or solid electrode is negative. This is believed to be due to the formation of a space charge in the space enclosed by the hollow electrode, as explained in the Smith application above referred to, alll paths available for conduction through the gas, except paths through the opening in the hollow electrode, being too short to permit ionization and conduction. In the illustrated embodiment. of the invention the electrodes have opposing surfaces separatedy a dist-ance comparable to the mean f ree path of electrons in the gas. The provision of an oxide coated carbon cathode in a tube of thischaracter decreases the voltage drop through the tube and increases the current carrying capa'city. This oxide coating may take thel form of an oxide of calcium, barium or strontium, or mixtures of these oxides, mixed with a rosin binder and burned onto the surface of the electrode, forming' a surface coatin k which functions as the active surface o the cathode. With a t ical tube of this construction it has been ound possible to pass two-tenths of an ampere with a volt-l age drop through the tube of one hundred twenty-live to one hundredA fifty volts approximatel The tube as illustrated is conveniently embodied in a simple form of rectifying circuit consisting of a source of alternating current initially indicated at 50 and included in .a rimary clrcuit 52 which is'inductively coup ed to a secondary circuit 56 including the recti 'n tube.

From t e ore oing it will bel evident that the lower end o the cathode constitutes an obstruction having a restricted opening for electrical discharge between the active cathode surface and the anode surface and that the space adjacent the active cathode surface (the interior of the hollow cathode) is isolated from the space adjacent the anode surface except through the aforesaid rcstricted o ening; also that the interior surface of the hollow cathode has, by virtue of the aforesaid coating, a lower work function than the exterior surface and that, owing to the location of the anode adjacent the opening in the hollow cathode, the electrical discharge is confined to that surface of the cathode having the low work function. y

The interior surface of the cathode 22, which constitutes the active cathode surface, and the upper surface of the anode 14, are obviously separated from each other b the obstructlon comprising disk 16 which orms a cover for the lower end ofthe cathode, the upper end of the cathode being closed by a cover integral with the peripheral wall of the cathode. Consequently the' s ace adjacent the interior active surface o the cathode-is isolated from the anode except that portion of the anode presented to the active cathode surface through the restricted openin in the cover 16. Y

a generic sense the term hollow cathode includes a cathode whose active surface only partially surrounds a aseous medium so that the medium imme iately adjacent the active surface is more or less pocketed or confined.

From the foregoing it will be evident that the tube 24, whlch defines a long narrow space between this tube and the tube 26, constitutes means for substantially prevent ing particles of the coating of the hollow cathode vwhich are dislodged from the .cathode during operation 4 rfrom reaching the wall of the tube 10.

From the foregoing it will be evident that the present invention is particularly applicable to gaseous conduction tubes of the type on the inside 'ated material from tem erature at which rectification is jdepen ent upon thermionic emission, as form an incandescent surface, since in these .socalled thermionic tubes the potential drop -is low and the cathode is not subjected to intense ion bombardment.

I claim:

1. A gaseous conduction device compris-` ing a sealed tube containing an obstruction having a restricted opening therethrough and an active cathode surface on one side of said obstruction, and an anode presented to said active cathode surfacethrou h said opening from thefother side of the o struction, said cathode surface comprising material having a low work function to increase electron emission and the space adacent the cathode surface being substantially isolated except through said restricted o enmg liberated during 'operation is substantially restricted to the region of gaseous conduction.

2. A gaseous conduction device com rising a hollow cathode with an opening t erein and an anode resented to the interior surface of the hol ow cathode through said opening, said surface havinr a substantially lower work function than ie exterior surface of the cathode, and means forv keeping said work function lower during operation of the tube.

3. A gaseous conduction device comprising a hollow cathode with a restricted openso that any of said material whic is said work function lower during operation of the tube, said means providing stantially confined to the mean free path of electron in the gas. l

4. A gaseous conduction r'e'ctiier employa gap subing an arrangement `of electrodes includlng a cathode which functions below the temperature at which rectification is de endent upon thermionic emission, the cathode being hollow and having an interior surface comprising material which aii'ords a low work function and which is partially liberated during operationand means for restraining liberated material from escapingrfrom the region of said surface.

5. A gaseous vconduction tube comprisin an anode, a cathode surface presented to sai anode, said surface being coated with material which adheres when vcold but is partially liberated during operation and which largely increases the electron emission, and means for substantially preventing the liber- 4 reaching the wallof the tube. y f

6. Gaseous conduction apparatus comprislas ing an anode, a hollow cathode having an interior surface presented to said anode, said surface comprising material which is liberated during operation and which largely increases the electron emission, and means to restrict the escape of said material when liberated.

7. A gaseous conduction tube comprising a hollow cathode with a restricted opening and an anode presented to the interior surface of the hollow cathode through said opening, said surface having a substantially lower work function than the exterior surface of the cathode, and means for substantially preventing particles which are dis- 

